Tactile sensors have conventionally been used for many applications; examples of such applications include robotic hands and skins, as well as biomedical sensing at human/machine interfaces (e.g., in prosthetic sockets). Various types of tactile sensors have conventionally been employed for these various applications. Examples of such tactile sensors include force sensitive resistors, capacitive sensors, optical sensors and MEMS sensors.
Many conventional tactile sensors can sense normal loads while being unable to sense shear loads. A normal load is a load perpendicular to a sensing surface. A shear load is a load parallel to the sensing surface. However, for many applications, it may be desirable to sense both normal loads and shear loads. For instance, in a robotic hand, shear load information can be used to enhance object manipulation and tactile exploration. Shear load information also has been seen to be important in monitoring prosthetic socket interface loads.
Some conventional approaches for multi-axis sensing are based on use of traditional strain gauge-based load cells, which are oftentimes large and expensive. Other conventional approaches for multi-axis sensing for tactile sensors use capacitive sensors, MEMS sensors, or optical sensors. For instance, a capacitive sensor can infer shear information of overlapping conductors through a dielectric. A MEMS sensor can include small cantilevers with piezo-resistive traces embedded in an elastomer; these sensors oftentimes have relatively small load capacity and are commonly frail. Conventional optical shear sensors oftentimes include a mechanical separation between an emitter and a photodiode so that the two are displaced relative to one another by shear loads. However, conventional optical shear sensors are unable to sense normal loads and typically are unable to differentiate between shear loads on differing axes.